The impacts of sleep variability on sleepiness, mood and cognitive functioning in young adults: an experimental study

Wanqi Sun, Forrest Tin Wai Cheung, Jiefan Ling, Xiaobo Yang, Jiaxin Wei, Ngan Yin Chan, Jihui Zhang, Chan, Yun Kwok Wing, Shirley Xin Li

Abstract

Introduction Sleep variability has often been reported in association with a wide range of impaired daytime functioning among young adults. However, current evidence, which was mostly based on the observational studies, could not delineate the causal relationship and underlying mechanisms. This study aimed to evaluate the impacts of experimentally induced variability in sleep duration on daytime sleepiness, mood and cognitive functioning in young adults.

Materials and Methods Thirty-six healthy young adults (16 males, aged 18-22 yrs) with habitual sleep duration over 7 hours per night, intermediate chronotype and no diagnosed sleep or psychiatric disorders were recruited. Before the experimental period, participants were asked to sleep at home on a regular schedule with 7.5h of time in bed (TIB) daily for a week with their sleep monitored by actigraphy. Participants subsequently underwent an 8-day protocol in the sleep laboratory consisting of two baseline nights with 7.5h of TIB, followed by either six nights of sleep with variable sleep schedule (TIB alternating between 6h and 9h on a daily basis for the variable sleep group) or fixed sleep schedule (TIB for 7.5h daily for the control group). Sleepiness, mood and cognitive functioning were measured in the morning and evening every day during the experimental period.

Results Participants in the variable sleep group reported a significantly higher level of daytime sleepiness on the days after 6 hours of sleep (day x condition: p=0.009), especially in the mornings (day x condition: p=0.005), as compared with the control group. Participants in the variable sleep group also had higher daily negative mood as compared with the control group particularly in the evenings at the margin of significance (day x condition: p=0.071). However, there were no significant differences in the positive mood and the performance on the cognitive tasks (i.e., sustained attention and processing speed) between the two groups.

Conclusion Our study found that moderate variability in daily sleep duration led to changes in daytime sleepiness and negative mood whilst daytime cognitive functioning was preserved. On the other hand, previous experimental studies showed that chronic sleep restriction followed by weekend recovery sleep might not be sufficient to restore impaired daytime functioning. Future studies should further explore the extent to which timely sleep compensation after sleep restriction, despite the induced sleep variability, could recover certain domains of functioning impairments.

Recommended citation: Sun, W., Cheung, T. W. F., Ling, J., Yang, X., Wei, J., Chan, N. Y., ... & Li, S. X. (2019). The impacts of sleep variability on sleepiness, mood and cognitive functioning in young adults: an experimental study. Sleep Medicine, 64, S367.